This application claims priority of European Application No. 00200883, filed on Mar. 13, 2000.
The field of art to which this invention pertains is that relating to a new composition based on an isocyanate-functional compound, an isocyanate-reactive compound, and a co-catalyst comprising a phosphine and a Michael acceptor.
There are many publications that disclose compositions comprising compounds capable of cross-linking or curing under appropriate conditions, such as when mixed with a catalyst, and their use, particularly as coating compositions.
For example, U.S. Pat. No. 5,084,536 discloses a coating composition comprising:
(a) compounds containing at least two unsaturated groups,
(b) compounds containing at least two groups having active hydrogen atoms of the type -SH, and
(c) a catalyst selected from, among others, phosphanes.
U.S. Pat. No. 3,729,404 discloses a curable composition comprising a polyene containing at least two reactive unsaturated carbon to carbon bonds per molecule and a polythiol containing at least two thiol groups per molecule. The curing takes place in the presence of a phosphine or phosphite.
U.S. Pat. No. 4,753,825 discloses isocyanate cross-linking with mercaptan groups under the influence of a vaporous amine catalyst to cure the coating composition.
EP-A-0 068 454 discloses a multi-pack coating composition comprising:
(a) an isocyanate component,
(b) an active hydrogen component, such as polythiol, and
(c) a Lewis base, such as tertiary phosphane.
Coatings used for painting various substrates, such as motor vehicles, are required to have physical properties such as good hardness, good mechanical strength, high drying rate, acceptable pot life, and good resistance to water, acids, and solvents. The coatings are also required to have good appearance properties, which means that films must be smooth and have a high gloss and high distinctness of image (DOI). It is also desirable that all properties be retained under prolonged outdoor weathering.
We have found new compositions that are superior to the prior art compositions with regard to achieving some or all of the above desired properties.
In brief summary, our invention is a composition comprising:
a) at least one isocyanate-functional compound comprising at least two isocyanate groups,
b) at least one isocyanate-reactive compound comprising at least two isocyanate-reactive groups selected from mercapto groups, hydroxyl groups, and mixtures thereof, and
c) a co-catalyst comprising a phosphine and a Michael acceptor.
In a second embodiment, our invention is a method of coating a substrate comprising coating the substrate with the above composition.
In a third embodiment, our invention is a substrate coated with the composition of the first mentioned embodiment.
In a fourth embodiment, our invention is an adhesive comprising the composition of the first mentioned embodiment.
Other embodiments of the invention encompass details about the compounds employed that comprise the claimed composition, the relative amounts thereof, the conditions appropriate for use of the composition, and the properties of the composition, all of which are hereinafter disclosed in the following discussion of each of the facets of the invention.
The catalysts included in the composition of the present invention for the cross-link reaction are a phosphine and a Michael acceptor, hence the name co-catalyst. The total amount of co-catalyst on the solid coating composition is preferably about 0.05 to about 20 wt. %, more preferably about 0.1 to about 15 wt. %, most preferably about 0.5 to about 10 wt. %. The co-catalysts are preferably used in a ratio of Michael acceptor groups to phosphine groups of about 0.05:1 to about 20:1, more preferably about 1:6 to about 6:1. The phosphine compound may preferably be used in a range of about 0.05 to about 20 eq. % on isocyanate-reactive groups, more preferably about 0.1 to about 15 eq. %, most preferably about 0.5 to about 10 eq. %. The Michael acceptor compound may be used in a range of about 0.05 to about 20 eq. % on isocyanate-reactive groups, more preferably about 0.1 to about 15 eq. %.
The isocyanates of the present invention comprise at least one isocyanate-functional compound. The isocyanate-functional compound can be an aromatic, aliphatic, cycloaliphatic and/or araliphatic isocyanate-functional compound optionally comprising heteroatoms such as oxygen and groups such as ester groups. The isocyanate-functional compound can also be an isocyanurate, uretdione, biuret, allophanate, an adduct, NCO prepolymers, or mixtures thereof.
Examples of suitable isocyanates to be used as the isocyanate-functional compound, or as starting materials for preparing an isocyanate-functional compound comprising an isocyanurate, biuret or uretdione structure include organic polyisocyanates represented by the formula
R(NCO)k 
wherein k is 2 or higher and R represents an organic group obtained by removing the isocyanate groups from an organic polyisocyanate having aromatically or (cyclo)aliphatically bound isocyanate groups. Preferred diisocyanates are those represented by the above formula wherein k is 2 and R represents a divalent aliphatic hydrocarbon group having 2 to 18 carbon atoms, a divalent cycloaliphatic hydrocarbon group having 5 to 15 carbon atoms, a divalent araliphatic hydrocarbon group having 7 to 15 carbon atoms or a divalent aromatic hydrocarbon group having 6 to 15 carbon atoms. Examples of organic diisocyanates which are particularly suitable include ethylene diisocyanate, 1,3-propylene diisocyanate 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 2-methyl-1,5-diisocyanate pentane, 2-ethyl-1,4-diisocyanate butane, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, isophorone diisocyanate, bis-(4-isocyanatocyclohexyl)-methane, 2,4xe2x80x2-dicyclohexylmethane diisocyanate, 1,3- and 1,4-bis(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methyl-cyclohexyl)-methane, 1-methyl-2,4- and -2 ,6-d ilsocyanato cyclohexane, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, xylene diisocyanate, xcex1,xcex1,xcex1xe2x80x2,xcex1xe2x80x2-tetramethyl-1,3- and -1,4-xylylene diisocyanate, 1,3- and 1,4-phenylene diisocyanate, 2,4- and 2,6-toluylene diisocyanate, 2,4xe2x80x2- and 4,4xe2x80x2-diphenylmethane diisocyanate, 1,5-diisocyanato naphthalene, and mixtures thereof. Aliphatic polyisocyanates containing 3 or more isocyanate groups such as 4-isocyanatomethyl-1,8-octane diisocyanate and lysine triisocyanate, and aromatic polyisocyanates containing 3 or more isocyanate groups such as 4,4xe2x80x2,4xe2x80x3-triphenylmethane triisocyanate, 1,3,5-triisocyanate benzene, polyphenyl polymethylene polyisocyanates obtained by phosgenating aniline/formaldehyde condensates, and mixtures thereof may also be used.
Examples of suitable polyisocyanates comprising an allophanate structure is include the above-mentioned organic polyisocyanates reacted with a mono- or polyalcohol.
Suitable mono- or polyalcohols which may be used to prepare the polyisocyanates containing allophanate groups include aliphatic, cycloaliphatic, araliphatic or aromatic mono- or polyalcohols. The mono- or polyalcohols may be linear, branched or cyclic, contain at least one carbon atom and have a molecular weight of up to 2500. The mono- or polyalcohols may optionally contain other hetero atoms in the form of, e.g., ether groups, ester groups, etc. However, the mono- or polyalcohols preferably do not contain hetero atoms other than the hydroxyl group(s). The molar ratio of mono- or polyalcohol to polyisocyanate is about 0.01 to about 0.5, preferably about 0.04 to about 0.2. Preferred mono- or polyalcohols are hydrocarbon mono- or polyalcohols and mono- or polyalcohols containing ether groups. The hydrocarbon mono- or polyalcohols preferably contain 1 to 36, more preferably 1 to 20, and most preferably 1 to 8 carbon atoms.
Examples of suitable monoalcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, t-butanol, n-pentanol, 2-hydroxy pentane, 3-hydroxy pentane, the isomeric methyl butyl alcohols, the isomeric dimethyl propyl alcohols, neopentyl alcohol, n-hexanol, n-heptanol, n-octanol, n-nonanol, 2-ethyl hexanol, trimethyl hexanol, decanol, dodecanol, tetradecanol, hexadecanol, octadecanol, 2,6,8-trimethyinonanol, 2-t-butyl-cyclohexanol, 4-cyclohexyl-1-butanol, cyclohexanol, benzyl alcohol, phenol, the cresols, the xylenols, the trimethylphenols, 2,4,6-trimethyl benzyl alcohol, branched chain primary alcohols and mixtures thereof (which are available from Henkel (Minneapolis, Minn.) under the xe2x80x9cSTANDAMUL(copyright)xe2x80x9d trademark) and mixtures of linear primary alcohols (which are available from Shell (Houston, Tex.) under the xe2x80x9cNEODOL(copyright)xe2x80x9d trademark).
Preferred ether-containing monoalcohols include ethoxy methanol, methoxy ethanol, ethoxy ethanol, the isomeric methoxy or ethoxy propanols, the isomeric propoxy methanols and ethanols, the isomeric methoxy butanols, the isomeric butoxy methanols, furfuralcohol and other monoalcohols which have a molecular weight of up to 2500 and are based on ethylene oxide, propylene oxide and/or butylene oxide. It is also possible in accordance with the present invention to use mixtures of the previously described monoalcohols.
Examples of suitable polyalcohols having two or more hydroxyl groups include ethane diol, 1,3-propanediol, 1,2-propanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, 1,3-butanediol, 1,6-hexanediol, neopentylglycol, glycerol, pentaerythritol, trimethylol propane, ditrimethylol propane, 1,4-cyclohexane dimethanol, the monoester of neopentylglycol and hydroxy pivalic acid, 2,2,4-trimethyl pentanediol, and dimethylol propionic acid, and mixtures thereof. Other preferred polyalcohols for the production of suitable polyurethanes include polyester and polyether diols having a number average molecular weight of less than 1000, for example the polyester diol prepared from I mole of phthalic anhydride and 2 moles of neopentyl glycol. It is also possible in accordance with the present invention to use mixtures of the polyalcohols and mixtures of a polyalcohol and the previously described monoalcohols.
Preferred isocyanates are the isocyanurate of hexamethylene diisocyanate and the isocyanurate of isophorone diisocyanate.
Examples of the isocyanate-reactive compound include a mercaptan-functional compound comprising at least two mercapto-functional groups, a hydroxyl-functional compound comprising at least two hydroxyl-functional groups, and a compound comprising at least one mercapto-functional group and one hydroxyl functional group. Also mixtures of these compounds may be used in the compositions of the present invention.
The mercaptan-functional compound comprising at least two mercapto-functional groups may be prepared by direct esterification of a mercapto-functional organic acid with a polyol. Examples of mercapto-functional organic acids include 3-mercaptopropionic acid, 2-mercaptopropionic acid, thio-salicylic acid, mercaptosuccinic acid, mercaptoacetic acid, or cysteine. Examples of compounds prepared according to such a method include pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (2-mercaptoacetate), trimethylol propane tris (3-mercaptopropionate), trimethylol propane tris (2-mercaptopropionate), and trimethylol propane tris (2-mercaptoacetate).
A further example of a compound prepared according to such a method consists of a hyperbranched polyol core based on a starter polyol, e.g., trimethylol propane, and dimethylol propionic acid. This polyol is subsequently esterified with 3-mercaptopropionic acid and isononanoic acid. These methods are described in European patent application EP-A 0 448 224 and International patent application WO 93/17060.
Other syntheses to prepare compounds comprising at least two mercapto-functional groups involve:
the reaction of an aryl or alkyl halide with NaHS to introduce a pendent mercapto group into the alkyl and aryl compounds, respectively;
the reaction of a Grignard reagent with sulphur to introduce a pendent mercapto group into the structure;
the reaction of a polymercaptan with a polyolefin according to a Michael addition reaction, a nucleophilic reaction, an electrophilic reaction or a radical reaction; and
the reduction of disulphides.
The most preferred mercapto-functional compound is pentaerythritol tetrakis (3-mercaptopropionate).
The hydroxyl-functional compound comprising at least two hydroxyl-functional groups may be selected from polyester polyols, polyether polyols, polyacrylate polyols, polyurethane polyols, cellulose acetobutyrate, hydroxyl-functional epoxy resins, alkyds, and dendrimeric polyols such as described in WO 93/17060. Also, hydroxyl-functional oligomers and monomers, such as castor oil and trimethylol propane, may be included. A preferred polyol is an acrylate polyol. More preferred is an acrylate polyol available from Bayer having the trade name Desmophen A450. This material is supplied in butyl acetate solution with a solids content of 50%, an OH value of 33 mg KOH/g, and an acid value of 4 mg KOH/g.
The compound comprising at least one mercapto-functional group and one hydroxyl-functional group may for example have a structure according to the following formula: T[(C3H6O)nCH2CHOHCH2SH]3, with T being a triol such as trimethylol propane or glycerol. An example of such a compound is commercially available from Henkel under the trademark Henkel Capcure(copyright) 3/800.
Alternatively, the compound comprising at least one mercapto-functional group and one hydroxyl-functional group may be a polyester prepared from (a) at least one polycarboxylic acid or reactive derivatives thereof, (b) at least one polyol, and (c) at least one mercapto-functional carboxylic acid. The polyesters preferably possess a branched structure. Branched polyesters are conventionally obtained through condensation of polycarboxylic acids or reactive derivatives thereof, such as the corresponding anhydrides or lower alkyl esters, with polyalcohols, when at least one of the reactants has a functionality of at least 3.
Examples of suitable polycarboxylic acids or reactive derivatives thereof are tetrahydrophthalic acid, tetrahydrophthalic anhydride, hexahydrophthalic acid, hexahydrophthalic anhydride, methyl hexahydrophthalic acid, methyl hexahydrophthalic anhydride, dimethylcyclohexane dicarboxylate, 1,4-cyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, phthalic acid, phthalic anhydride, isophthalic acid, terephthalic acid, 5-tert. butyl isophthalic acid, trimellitic anhydride, maleic acid, maleic anhydride, fumaric acid, succinic acid, succinic anhydride, dodecenyl succinic anhydride, dimethyl succinate, glutaric acid, adipic acid, dimethyl adipate, azelaic acid, and mixtures thereof.
Examples of suitable polyols include trimethylol propane, trimethylol ethane, glycerol, 1,2,6-hexanetriol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methylpropane-1,3-diol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propane diol, cyclohexane-1,4-dimethylol, the monoester of neopentyl glycol and hydroxypivalic acid, hydrogenated Bisphenol A, 1,5-pentanediol, 3-methyl-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl pentane-1,3-diol, dimethylol propionic acid, pentaerythritol, di-trimethylolpropane, dipentaerythritol, and mixtures thereof.
Examples of suitable mercapto-functional organic acids include 3-mercaptopropionic acid, 2-mercaptopropionic acid, thio-salicylic acid, mercaptosuccinic acid, mercaptoacetic acid, cysteine, and mixtures thereof.
Optionally, monocarboxylic acids and monoalcohols may be used in the preparation of the polyesters. Preferably, C4-C18 monocarboxylic acids and C6-C18 monoalcohols are used. Examples of the C4-C18 monocarboxylic acids include pivalic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, 2-ethyl hexanoic acid, isononanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, isostearic acid, stearic acid, hydroxystearic acid, benzoic acid, 4-tert. butyl benzoic acid, and mixtures thereof. Examples of the C6-C18 monoalcohols include cyclohexanol, 2-ethylhexanol, stearyl alcohol, and 4-tert. butyl cyclohexanol.
The phosphine employed as one of the co-catalysts is a compound according to the formula Z(PR2)n, wherein n is an integer of 1 to 6, R is independently selected from an aryl group or (cyclo)alk(en)yl group which may be linear or branched and may or may not contain one or more heteroatoms such as oxygen atoms and halogen atoms, provided that the oxygen heteroatoms are not directly linked to a phosphorus atom.
Preferably, R is an alkyl or aryl group, more preferably the alkyl group has 1 to 15 carbon atoms and the aryl group has 6 to 15 carbon atoms.
In the event that n=l, Z is a group according to R. Such compounds are hereinafter referred to as monophosphines. Examples of monophosphines include triphenyl phosphine and trioctyl phosphine.
In the event that nxe2x89xa72, Z is selected from an arylene group, (cyclo)alk(en)yl(id)ene group which may be linear or branched and may or may not contain heteroatoms such as oxygen, phosphorus, nitrogen, provided that the oxygen and nitrogen heteroatoms are not directly linked to a phosphorus atom, and/or groups selected from carboxyl, anhydride, cycloalkyl, aryl or may be a single bond. These compounds are hereinafter referred to as polyphosphines. Examples of the polyphosphines include bis (2-diphenylphosphinoethyl) phenylphosphine, 1,4-bis (diphenylphosphino) butane, bis (diphenylphosphino) methane, 1,3-bis(diphenylphosphino)propane, 1,5-bis (diphenylphosphino) pentane, trans-1,2-bis (diphenylphosphine) ethylene, cis-1,2-bis (diphenylphosphino) ethylene, (R)-(+)-2,2xe2x80x2-bis (diphenylphosphino)-1,1xe2x80x2-binaphtyl, tetraphenylbiphosphine, tris 2-(diphenylphosphino) (ethyl) phosphine, 1,1-bis (diphenylphosphino) ethylene, 1,1,1-tris (diphenylphosphinomethyl) ethane, 2,3-bis (diphenylphosphino) maleic anhydride, 1,2-bis (diphenylphosphino) benzene, 1,2-bis (pentafluorophenyl) (phosphino) ethane, (2R,3R)-(xe2x88x92)-2,3-bis (diphenylphosphino) bicyclo [2.2.1] hept-5-ene, and ethylene-bis (2-methoxyphenyl) (phenylphosphine). Preferred are polyphosphines wherein Z is a alkylene group, linear or branched, having 1 to 8 carbon atoms optionally comprising a phosphorus atom and R is an aryl group. The most preferred phosphines are 1,4-bis (diphenylphosphino) butane or triphenylphosphine.
The Michael acceptor preferably comprises one or more olefinically unsaturated groups, the olefinically unsaturated group comprising at least one electron-withdrawing functionality linked to a carbon atom of the unsaturated bond. The olefinically unsaturated bond may be a double or a triple bond. Preferably, the Michael acceptor has a structure according to the following formula I: 
wherein at least one of R1, R2, R3, and R4 comprises an electron-withdrawing functionality linked to a carbon atom of the unsaturated bond and m is an integer from 1 to 6.
Examples of the electron-withdrawing functionality include carbonyl, carboxyl, ester, thiocarbonyl, thiocarboxyl, thioesters, sulfoxide, sulfonyl, sulfo, phosphate, phosphite, phosphonite, phosphinite, nitro, nitrile, and amide.
In the event that m is 1, at least one of R1, R2, R3, and/or R4 comprises the electron withdrawing functionality and the electron-withdrawing functionality may be attached to a hydrogen atom, linear or branched alkyl, cycloalkyl, alkenyl, cyclo-alkenyl, alkynyl, cyclo-alkynyl, and aryl which may optionally be substituted with various other functionalities, such as carboxylic acid or hydroxide. If they do not comprise an electron-withdrawing functionality, R1, R2, R3, and/or R4 may be independently selected from a hydrogen atom, linear or branched alkyl, cycloalkyl, alkenyl, cyclo-alkenyl, alkynyl, cyclo-alkynyl, and aryl which may optionally be substituted with various functionalities, such as carboxylic acid or hydroxide. R1 and R3 or R2 and R4 may also form a ring comprising one or more electron withdrawing functionalities.
In the event that m is 2 to 6, R1 is selected from a simple bond, an electron withdrawing functionality, and a polyvalent group derived from a hydrocarbon compound optionally comprising hetero atoms such as xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94Sixe2x80x94, and xe2x80x94Pxe2x80x94, groups such as amide, urea, and ester groups, and/or one or more electron withdrawing functionalities. The hydrocarbon compound 10 may be a substituted or unsubstituted alkane, cycloalkane, alkene, cycloalkene, alkyne, cycloalkyne, arene, or combinations thereof. The polyvalent group is preferably derived from a polyalcohol. Examples of such polyalcohols include trimethylol propane, trimethylol ethane, glycerol, 1,2,6-hexanetriol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methylpropane-1,3-diol, neopentyl glycol, 2-butyl-2-ethyl-1,3-propane diol, cyclohexane-1,4-dimethylol, the monoester of neopentyl glycol and hydroxypivalic acid, hydrogenated Bisphenol A, 1,5-pentanediol, 3-methyl-pentanediol, 1,6-hexanediol, 2,2,4-trimethyl pentane-1,3-diol, dimethylol propionic acid, pentaerythritol, di-trimethylolpropane and dipentaerythritol. Alternatively, R3 may also form a ring with R1 comprising one or more electron withdrawing functionalities.
Examples of Michael acceptors are isobornyl acrylate, isooctyl acrylate, 2,2xe2x80x2-methylene bis (6-t.butyl 4-methyl phenol) monoacrylate, phenoxyethyl acrylate, lauryl acrylate, dicyclopentadiene acrylate, N-butyl maleimide, benzyl acrylate, trimethylol propane tri-acrylate, maleic anhydride, a trifunctional adduct of isophorone diisocyanate and 2-hydroxyethyl maleimide, diethyl maleate, methoxypropyl citraconimide, diethylbenzylidene malonate, or an o,p-unsaturated aldehyde, e.g., cinnamaldehyde or citral. The most preferred Michael acceptors comprise trimethylol propane triacrylate, Irganox 3052 or N-butyl maleimide.
The ratio of isocyanate groups to thiol groups and/or hydroxyl groups is between about 0.5:1 and about 3:1, preferably about 0.8:1 to about 2:1.
The composition according to the present invention may be a water borne composition, a solvent borne composition or a solvent-free composition. Since the composition may be composed of liquid oligomers, it is especially suitable for use as a high-solids composition or a solvent-free composition. Preferably, the theoretical volatile organic content (VOC) in the composition is less than about 450 g/l, more preferably less than about 350 g/l, most preferably less than about 250 g/l.
The composition may contain pigments, effect pigments such as aluminium parts, UV absorbers, adhesion promoters such as epoxy silane, HALS-type stabilizers, flow additives or other additives.
The present compositions are of particular interest in coating compositions or adhesives. Preferably, a two-pack composition is used. Preferably, the first component of the two-pack coating or adhesive comprises the compound comprising two or more isocyanate-functional groups as well as one of the co-catalysts, while the second component of the composition comprises the compound comprising the isocyanate-reactive groups and the other co-catalyst.
The composition according to the present invention can be applied by conventional methods, including spraying, brushing, roller coating or dipping. The composition of the present invention is also suitable for application by an external mixing apparatus, one wherein a liquid composition comprising at least one isocyanate-functional compound, at least one isocyanate-reactive compound and the phosphine compound of the co-catalyst is sprayed via a spray nozzle, with a small amount of a liquid catalyst composition comprising a Michael acceptor. Such an apparatus is described, for example, in WO 98/41316. Due to the very effective use of the catalysts, the compositions according to the present invention have very short curing times, which makes this method specifically suitable for these compositions.
The composition according to the invention can be used on various substrates, in particular wood, plastics, and metal substrates such as aluminium, steel, or galvanized steel, for industrial applications of any kind. The composition can be used for instance as an adhesive or as a coating, e.g., as a putty, primer, filler, base coat, top coat or clear coat. Since it is easily sprayable, can be applied at ambient temperatures, and the resulting coating has a high gloss, the composition is especially useful in the refinish industry, in particular the body shop, to repair automobiles and in the automotive industry for the finishing of large transport vehicles, such as trains, buses, and airplanes. Most preferred is the use thereof as a car repair coating. Generally in car repair, several layers need to be applied, such as a primer, a filler, a base coat, and a clear coat. Because of the short drying times, a next layer can be applied within a short time from applying the first layer.
The following examples are presented to illustrate the present invention and are not intended to unduly restrict the scope and spirit of the claims attached hereto.